The present invention is directed to a bone screw of the type wherein a head of the bone screw is swingable or can swivel about the shank of the bone screw until the surgeon is satisfied with the relative placement of the two parts and thereafter the head can be locked in position relative to the shank.
Bone screws are utilized in many types of spinal surgery in order to secure various implants to vertebrae along the spinal column. Bone screws of this type typically have a shank that is threaded and adapted to be implanted into a vertebral body of a vertebrae. The bone screw also includes a head which is designed to extend beyond the vertebrae and which has a channel to receive another implant. Typically the channel will receive a rod or a rod-like member. In bone screws of this type, the head may be open, in which case a closure must be used to close between opposite sides of the head once a rod-like implant is placed therein, or closed wherein a rod-like implant is threaded through the head of a bone screw.
When the head and shank of the bone screw are fixed in position relative to each other, it is not always possible to insert a bone screw in such a manner that the head will be in the best position for receiving other implants. Consequently, swivel head bone screws have been designed that allow the head of the bone screw to rotate or swivel about an upper end of the shank of the bone screw while the surgeon is positioning other implants and finding the best position for the bone screw head. However, once the surgeon has determined that the head is in the best position, it is then necessary to lock or fix the head relative to the shank and different types of structures have been previously developed for this purpose. Unfortunately, the prior art devices have a tendency to be bulky, slip under high loading or require many parts.
It is desirable to have a swivel head bone screw that can be captured by the shank prior to locking of the head, but that allows the head to freely swivel or pivot about a top of the shank prior to locking. It is then further desirable to have the head that can be fixably locked in a configuration or position relative to the shank where the head best fits with other elements of the overall spinal implant.
Furthermore, it is desirable to maintain the number of parts of the device at a minimum. Also, it is desirable to secure the various parts together in such a way, so that, if parts become loose under use for some reason, the device will not totally disassemble.